The invention relates to an amplification device comprising a first and a second amplifier arranged in cascade, each amplifier having a gain proper and being provided with a feedback loop.
Such a device is described on page 223 of the manual xe2x80x9cDesign with Operational Amplifiers and Analog Integrated Circuitsxe2x80x9d by Mr. Sergio Franco, published by McGraw-Hill International.
In this document, it is recommended to equitably distribute the gain of the device as a whole among the two amplifiers, i.e. assign identical values to the gain proper of the first amplifier and the second amplifier, with a view to obtaining the largest possible passband for the device.
This document does not make mention of the linearity characteristics of the amplification device. Now, in most applications where amplification of a signal is necessary, the value of the amplified signal should develop linearly with respect to the value of the signal to be amplified, which means that the risk of distortions being caused in the amplified signal leading to changes in the information that it conveys has to be accepted.
It is an object of the invention to optimize the performance in terms of linearity of an amplification device comprising two stages, while preserving an acceptable passband.
The inventors have actually discovered that the gain distribution customarily recommended to optimize the passband does not lead to the best possible linearity for the amplification device. In accordance with this invention, an amplification device as described in the opening paragraph is characterized in that the value of the inverse of the gain proper of the first amplifier is substantially equal to three times the value of the inverse of the gain proper of the second amplifier raised to the third power.
It will be demonstrated hereinafter that said choice causes the value of the linearity of the amplification device to be maximized.
Of course, numerous embodiments of the first and second amplifiers are possible and known to those skilled in the art.
In accordance with one of these embodiments, each amplifier comprises an operational inverting amplifier.
In accordance with another embodiment, each amplifier includes an operational non-inverting amplifier.
In other embodiments, each amplifier may itself be composed of a plurality of amplifiers arranged in cascade.
The scope of the invention is so wide that it includes innumerable applications, such as, for example, the amplification of signals within television receivers, decoder housings or even within radiotelephones. Thus, the invention also relates to a device for receiving radioelectric signals, comprising:
an antenna system for receiving such a signal and transforming it to an electronic signal, commonly referred to as radio signal,
a frequency converter intended to supply an intermediate signal, representative of the radio signal, having a so-called intermediate frequency,
an amplification device as claimed in claim 1, intended to supply an amplified intermediate signal,
a demodulator intended to demodulate the signal supplied by the amplification device, and
a signal processor intended to exploit the demodulated signal.